Mobile electronic devices such as mobile telephones and tablet computers require extensive power management circuitry. For example, mobile electronic devices often include multiple switching power converters, such as for controlling battery charging and for providing point-of-load regulation for processors and other integrated circuits. Power management circuitry often occupies a signification portion, e.g., up to 40%, of a mobile electronic device's volume.
Switching power converters typically include one or more inductors to store energy in magnetic form. For example, a buck DC-to-DC converter includes an inductor as part of an output filter for removing AC components from the converter's switching waveform. Inductors are typically among the largest components within DC-to-DC converters. Therefore, it is desirable to minimize inductor size. However, it is difficult to reduce inductor size without degrading inductor performance and/or significantly increasing inductor cost. For example, reducing the cross-sectional area of an inductor's magnetic core typically increases the magnetic core's reluctance, thereby increasing core losses. As another example, decreasing winding cross-sectional area increases the winding's DC resistance, thereby increasing copper losses.
It is known that a single coupled inductor can replace multiple discrete inductors in a switching power converter, to improve converter performance, reduce converter size, and/or reduce converter cost. Examples of coupled inductors and associated systems and methods are found in U.S. Pat. No. 6,362,986 to Schultz et al., which is incorporated herein by reference. Some examples of coupled inductor structures are found in U.S. Patent Application Publication Number 2004/0113741 to Li et al., which is also incorporated herein by reference.
In contrast to discrete inductors, coupled inductors have two distinct inductance values, i.e., magnetizing inductance and leakage inductance. Magnetizing inductance is associated with magnetic coupling of the windings and results from magnetic flux generated by current flowing through one winding linking each other winding of the coupled inductor. Leakage inductance, on the other hand, is associated with energy storage and results from magnetic flux generated by current flowing through one winding not linking any of the other windings of the coupled inductor. Both magnetizing inductance and leakage inductance are important parameters in switching power converter applications of coupled inductors. Specifically, leakage inductance values typically must be within a limited range of values to achieve an acceptable tradeoff between low ripple current magnitude and adequate converter transient response. The magnetizing inductance value, on the other hand, typically must be significantly larger than the leakage inductance values to achieve sufficiently strong magnetic coupling of the windings, to realize the advantages of using a coupled inductor instead of multiple discrete inductors.
While use of a coupled inductor in a switching power converter offers many advantages, conventional coupled inductors typically having a higher profile (height) than discrete inductor counterparts. Many mobile electronic devices, though, have stringent low-profile requirements, often dictating that component profile not exceed one millimeter. Therefore, coupled inductor have not obtained large market share in low-profile applications. Additionally, conventional coupled inductors are often more expensive than discrete inductors having similar properties, and therefore coupled inductors are not widely used in low-current, i.e., less than 10 amperes per phase, applications.